The present invention relates to a novel optically functional element, its production method and various applications using the same. In particular, the present invention relates to an optically functional element applicable to an optical switch with a large change in refractive index with temperature, temperature sensor and optical information recording medium, along with a production method for the same.
Optically functional materials, of which optical characteristics such as transmittance and refractive index change by exterior field such as light, temperature and electric field, have been used as elements such as optical switch, optical modulator, light amplifier, wavelength selective element, optical soliton element, optical information recording medium, temperature sensor and electro-optical element.
Examples of materials with a transmittance changeable by exterior field include such as photochromism, thermochromism and electrochromism materials. In these materials, transmittance can be changed reversibly by an application of light, temperature and electrical field, respectively, correspondingly to their intensity, and thus they are used as optical switch, temperature sensor, masking layer for optical information recording medium and the like by shielding transmitted light or controlling spot diameter of transmitted light. As examples of these materials, the following are known: Organic photochromism materials such as derivatives of triphenylmethan, azobenzene and spiropyran disclosed in JP-A-7-20600, organic or inorganic thermochromism materials such as N-salicylideneaniline, AgHgI4 and Cu2HgI4, along with materials in which these materials are dispersed in dielectric materials having different refractive indices.
On the other hand, as examples of materials with refractive index changeable by exterior field, second or third order non-linear optical materials are known, of which refractive indices change at a part applied with laser or electric field. As second order non-linear optical materials, the following are known: Organic materials such as nitropyridine derivatives and methylnitroaniline (MNA) and inorganic dielectric materials such as KNbO3 and LiNbO3, which have been used as optical switch, electro-optical element and the like. Third order non-linear optical materials include glass dispersed with semiconductor fine particles such as CuCl and CdS, which have been used as optical switch of light waveguide type wavelength selection element and light pulse generating element (See xe2x80x9cHandbook of Optical Materialsxe2x80x9d: published by Realize Co., Ltd., 1992).
In addition, as materials with refractive index changeable with temperature, zinc based semiconductor materials such as ZnS and ZnSe and finely powdered PbS are known. Providing that amount of change in refractive index with temperature, xcex94nT, is expressed by the following formula:       Δ    ⁢          xe2x80x83        ⁢          n      T        =      "LeftBracketingBar"                  Δ        ⁢                  xe2x80x83                ⁢        n                    Δ        ⁢                  xe2x80x83                ⁢        T              "RightBracketingBar"  
wherein,
xcex94n is amount of change in refractive index; and
xcex94T is amount of change in temperature
these materials have been reported to have xcex94nT from about 5.95xc3x9710xe2x88x925/xc2x0 C. to about 1.47xc3x9710xe2x88x924/xc2x0 C. (See Physics Report, Vol. 46, No. 12, December 1997).
Further, as non-linear optical materials, the following are known: Those using Co3O4 and CoO as targets disclosed in JP-A-10-340482, amorphous metal oxides containing fine particles of Fe, Ni and Co disclosed in JP-A-5-224262 and substrates on which thin films of oxides of one or more elements of V, Cr, Mn, Fe, Ni, Co and Cu are formed as disclosed in JP-A-7-248516.
Since temperature sensor or device performing optical switching with temperature mainly works based on thermochromism switching as described above, amount of transmitted light varies. Therefore, they have not been suitable for a communication device in which such change gives unfavorable effects. Presently known devices made of materials whose refractive index changes with temperature have small change in refractive index and have been difficult to get sufficient change as switching or temperature sensor. Furthermore, these materials have response rate of refractive index with temperature in ms level, which is still slow in communication or light recording fields and thus have not been suitable to these applications.
Examples in the references of the above described xe2x80x9cPhysics Reportxe2x80x9d also required to be used as a dispersion in solvent due to powder form, which has made it difficult to be used as a thin film.
Furthermore, in optical switching also, these elements have had difficulty in characteristics control so as to have energy sufficient to raise change in refractive index or transmittance in these elements and to give incident laser light for stable output. The above patents do not disclose change in refractive index responsive to temperature, crystal particle size and crystal structure of oxide thin films.
Objectives of the present invention are to provide an optically functional element having large change in refractive index responsive to temperature change, its production methods and various applications using the same.
In an optically functional element with optically functional thin film on a substrate, the present invention is characterized in comprising at least one of the following: Said thin film consists of oxides and is composed of columnar crystal having average diameter of not larger than 13 nm, preferably not larger than 7 nm, said thin film consists of oxides and a change in average refractive index of 633 nm laser light from room temperature to 300xc2x0 C. is not less than 2xc3x9710xe2x88x924/xc2x0 C., said thin film consists of oxides and is composed of columnar crystal inclined against said substrate surface, said thin film mainly consists of oxides of one or more types of Co and Fe having spinel structure and is composed of columnar crystal, and at least one type of Co and Fe of said thin film mainly consists of M3O4 oxides including not less than one oxide of Si, Ti, Al, Te, alkaline metals and alkaline earth metals and is composed of columnar crystal.
The present invention is further characterized in a production method for an optically functional element to form optically functional thin film consisting of oxides on a substrate, wherein said thin film is formed by sputtering under reduced pressure of inert gas atmosphere having 3-15% by volume of oxygen.
The present invention is characterized in an optical switch equipped with a light receiver to receive light introduced from light source and an optically functional element having optically functional thin film to alter light pass of said light, wherein said optically functional element is consisted of the above described optically functional element.
The present invention is characterized in a temperature sensor equipped with a light receiver to receive light introduced from light source and an optically functional element having optically functional thin film to alter light pass of said light, characterized in that said optically functional element is consisted of the above described optically functional element.
The present invention is characterized in a substrate with information formed by pits and recording medium of optical information to provide output of said information by reflection light from light reflection film formed on said substrate, wherein said reflection film has, at its incident side of light, an optically functional thin film having refractive index changeable depending on incident light intensity and said thin film is consisted of the above described thin film.
An optically functional thin film formed in an optically functional element of the present invention, is formed on a substrate directly or via other layers, which is composed of fine particles with average particle diameter of not larger than 13 nm observed at film surface and its refractive index changes in response to own temperature change. The above described change in refractive index, xcex94nT, expressed by the following formula:       Δ    ⁢          xe2x80x83        ⁢          n      T        =      "LeftBracketingBar"                  Δ        ⁢                  xe2x80x83                ⁢        n                    Δ        ⁢                  xe2x80x83                ⁢        T              "RightBracketingBar"  
wherein,
xcex94n is amount of change in refractive index; and
xcex94T is amount of change in temperature;
is preferably not smaller than 2.0xc3x9710xe2x88x924/xc2x0 C. and that change is preferably completed in not slower than 1xc3x9710xe2x88x927/xc2x0 C. after completion of temperature change.
The above described particles have standard deviation of particle size of not larger than 30% of said average particle diameter and are columnar particles grown in an angle from 45 degree to 90 degree against interface between said thin film and substrate and grain boundary phase are formed at interfaces among particles. More preferably, the above described average particle diameter is not larger than 6 nm.
Said thin film is oxide-based one containing at least Co or Fe, more preferably crystalline fine particles containing Co or Fe and having spinel structure, and said grain boundary phase contains at least one types of element selected from a group consisting of at least Si, Ti, Al, Te, alkaline metals and alkaline earth metals. Furthermore, said tin film contains Co or Fe element in amount of 60-95% by weight as of oxide form, M3O4 (M=CO or Fe).
The above optically functional thin film is produced by forming said thin film on a substrate by sputtering target material surface with plasma generated on the target material, wherein, oxygen of not higher than 3-10% by volume is contained in said plasma formed in inert gas under reduced pressure.
Optical switch element of the present invention has an optical switch which is placed at optical pass and alters optical pass by change in temperature and temperature control mechanism, placed around the optical switch, to regulate element temperature. This optical switch changes temperature of itself in response to temperature control mechanism, which induces reversible change in refractive index in such a manner of amount of refractive index change, xcex94nT, and response time as described above.
The above optical switch is a thin film formed directly on a substrate or via other layers, which contains Co or Fe, is composed of an assembly of fine crystalline particles with a diameter of not less than 2 nm and not larger than 20 nm, where grain boundary phase is as described above.
Temperature sensor of the present invention is one to measure ambient temperature and composed of at least light source, light introduced from the light source, light receiver of the light and sensor section placed at light pass to alter light pass with change in ambient temperature. The sensor section reversibly changes refractive index by change in own temperature and has an amount of refractive index change, xcex94nT, and response time needed to change from an original refractive index, n0, to a different refractive index after temperature change, as described above.
Thin film is formed at said sensor section is as described above. Said fine particles have diameter of preferably 2-200 nm and contains Co or Fe.
Thin film in accordance with the present invention preferably has a thickness of 25-100 nm and formed with a little inclination against substrate surface and formed by precipitation unidirectionally in columnar shape.